Untitled

public class Purchase {

    private SalableBook[] items;
    private int itemCounter;
    private String date;

    public Purchase(int count, String date) {
        items = new SalableBook[count];
        this.date = date;

    }

    public void addItem(SalableBook sobj) {
        if (this.itemCounter < this.items.length) {
            this.items[itemCounter++] = sobj;

        } else {
            System.out.println("Purchase is full");
        }
    }

    public SalableBook getBook(int index) {
        if (index >= 0 && index < items.length) {
            return items[index];

        }
        return null;
    }

    public double sump() {
        double sum = 0;
        for (SalableBook b : items) {
            sum += b.computeCost();
        }
        return sum;
    }

    public String getInfo(int index) {
        SalableBook book = getBook(index);
        String info = "";
        if (book != null) {
            if (book instanceof ElectronicBook) {
                ElectronicBook ebook = (ElectronicBook) book;
                info += "size:" + ebook.getSize() + ", URL:" + ebook.getUrl();
            } else if (book instanceof PaperBook) {
                PaperBook pbook = (PaperBook) book;
                info += "weight: " + pbook.getWeight() + ", quantity: " + pbook.getQuantity();

            }
        }
        return info;
    }

    public String toString() {
        String s = "\n Listing of item in the purchase " + this.date + "\n";
        for (SalableBook p : this.items) {
            s += "\n \t-" + p + "\n";
        }
        s += "End of list of book";
        return s;
    }
}